1. Field Of The Invention
This invention relates to the valve train of an internal combustion engine and specifically to a lash cap for the poppet valve in a four stroke engine.
2. Description Of The Prior Art
Four stroke internal combustion engines have two or more intake and exhaust valves that are frequently configured in the shape of a poppet valve in which a mushroom shaped head is attached to a long stem. The valve stem fits within a valve guide placed or formed in the cylinder head and terminates in a groove or grooves at its distal tip. These grooves are used to retain conical valve keepers that are used to lock a valve spring retainer against the force of a valve spring serving to close the valve. The valve is opened through the use of a rocker arm or follower that is remotely operated by a camshaft designed to time the opening and closing of the valve to provide the appropriate performance parameters for the engine.
Modern high performance engines incorporate valves that are made of a variety of materials, including titanium, to provide the appropriate combination of strength, lightness and resistance to heat necessary for long life and high performance. However, when materials such as titanium are used for such valves, they may be damaged when pushed on by the valve actuating mechanism, since it is not easily or simply accomplished to provide a hardened surface on the distal end of the valve itself, as is the case when steel valves areas used. For this reason, lash caps have been developed to be placed over the distal end of the valve stem. These lash caps are made of hardened steel and provide a larger area upon which the valve actuating mechanism may push and protect the relatively soft tip of the distal end of the valve stem. However, such lash caps could sometimes become dislodged when the engine was operated at very high speed, thereafter failing to protect the distal end of the valve stem and also distributing a loose foreign object in the engine that might cause considerable damage unless the engine was stopped.
Previous methods to prevent the dislodging of lash caps included increasing the depth of the cup fitting over the distal end of the valve to thereby make it harder for the lash cap to become dislodged or increasing the diameter of the lash cap to make it less likely that it would cock and come loose from the distal end of the valve stem. However, both of these methods did not result in a positive retention of the lash cap in the valve train assembly and further unnecessarily added to the weight of the valve train, an undesirable effect in high performance applications.
There remains, therefore, a need for a means of positively retaining lash caps for the distal end of poppet valves in high performance applications that is simple, reliable, relatively lightweight and not prone to failure at high speed.